LR White:A convenient and economical premixed resin with very
wide application. Being both hydrophilic and electron beam
stable it is equally suitable for light and electron
microscopy, and with appropriate fixation the same specimen
may be used for both techniques. Published work shows that
immunocrytochemical methods may be used through LR White
sections without etching or any pre-treatment.

When using LR White embedding resin
for dedicated electron microscopy, very few changes need to
be made to the regime used for epoxy resin embedding. Every
laboratory has its own individual embedding schedule but we
have laid out a Typical Schedule for LR White as guidance for
its use included to the Kits.

Resin embedding for
light microscopy provides greatly improved cellular
definition compared to paraffin embedding, and for this
reason is now widely used in diagnoses particularly of Renal
disease, Lymphomas and bone marrow trephines, as well as
research.

The acrylic resins currently used however are not suitable
for E.M. and the eooxy resins used for E.M. are not easily
stained for light microscopy. LR White, however, can be used
for both purposes and lymph node for example (12x10x3mm) can
be processed, cut and stained for light microscopy, the same
block trimmed down, cut and staied for electron microscopy.

LR White can also be used for the histochemical
demonstration of some of the more resistant enzymes, and for
the immunocytochemical demonstration of intracellular
immunoglobulins.

For those laboratories already using an acrylic ressin
e.g. HEMA or Glycol Methacrylate no alteration need be made
to the current processing schedule, but we have laid out a
typical schedule for LR White as guidance for its use
included to the Kits.

L.R. White resin has
five advantages which can be exploited for the localisation
of antigens in sections of fixed and embedded tissue under
the electron microscope.

It is a hydrophilic embedding agent which means that
ultrathin sections allow the passage of aqueous solutions
even at neutral pH as opposed to epoxides and polyesters,
ultra-thin sections of which are much less permeable.

Its lipid solvency is apparently low for a plastic
embedding agent and therefore membrane and cytosol structures
can be observed under the electron microscope even when
osmium has not been used to stablise lipids. No low
temperature methods are required although tissue structure is
much improved by perfustion fixation methods.

It does not, where it has so far been tested, prevent the
demonstration of antigens by immunochemical techniques. No
etching or protease digestion has so far been necessary.

It is beam-stable, standing up well to even quite low KVs,
thus representing a considerable advance over the more
commonly used methacrylates.

It tolerates rapid, partial dehydration, accepting tissue
from 70% ethanol. Such tissue has an improved antigenicity
over tissue which has been fully dehydrated.

Sections from L.R. White
embedded tissue have been used sucessfully for
immunocytochemistry at both the light microscope and electron
microsope levels. This demonstrates quite clearly that the
visualizetion steps of the immunocytochemical procedure will
penetrate the resin and react with tissue antigens if they
have been preserved in the tissue.

Much interest has centered on using immunocytochemistry to
detect protein hormones and the various classes of
immunoglobulin and generally these classes of antigen have
proved resistant to alteration both in processing to
paraffin-wax an to L.R. White resin.

It is the special hydrophilic nature of L.R. White which
allows immunochemicals to permeate the supporting resin and
reach its sites of binding and no resin pertreatement is
necessary, or indeed possible, to faciliate this penetration.

We have been sucessful with L.R. White blocks only when
they have been thermally cured, probably because when
accelerator-curing the resin the exotherm produced is
sufficient to damage the integrity of the tissue antigen.
Some workers have also reported that a slight under-cure of
L.R. White, say at 50° for 20-24hr aids subsequent
penetration of antisera, but we have obtained good results
without deviating from the standard polymerisation schedule.
The guidance included.

Using LR White for Hard Tissue
(Picture: Bone from Human Mandible)

LR White can be used for
the microtomy of decalcified bone and teeth and also for
microtomy or sawing and grinding of undecalcified tissues.

Decalcified Tissue: May be processed, cut
and stained similarly to soft tissue (see Using LR White for
Light Microscopy), except that dehydration and infiltration
times may need to be extended depending on the size of
tissue. It is also recommended that bone be de-fatted to
imporove the penetration of resin into marrow cavities. This
can be be achieved by using chloroform after dehydration,
returing to absolute alchohol to remove the chloroform before
infiltrating with resin and polymerising.

Undecalcified Tissue: Dehydration and
infiltration times will vary depending on size and density of
tissue. Those laboratories using Methyl or Butyl methacrylate
at present can use similar dehydration times, but
infiltration will probably be shortened due to the low
viscosity of the resin.

LR
Gold: A Special acrylic resin for very
special purposes. Its infiltration and polymerisation at low
tempperatures down to−20℃ means that unfixed tissue may
be embedded in LR Gold. This enables enzyme histochemistry
and immunocytochemistry of many fixation sensitive enzymes
and epitomes to be performed on １〜２µｍ resin
setions. Bringing the quality of resin histology to an area
where only cryostat setions were previously available. LR
Gold is a real step forward in histochemial technique. This
resin has the ability to be cured by blue light thus making
expensive ultra-violet light sources required by other
systems unnecessary.